On 28/11/2024 11:02, Boris Brezillon wrote:
> When the runtime PM resume callback returns an error, it puts the device
> in a state where it can't be resumed anymore. Make sure we can recover
> from such transient failures by calling pm_runtime_set_suspended()
> explicitly after a pm_runtime_resume_and_get() failure.
>
> v2:
> - Add a comment explaining potential races in
> panthor_device_resume_and_get()
Thanks for the comment, see below.
>
> Signed-off-by: Boris Brezillon <boris.brezillon@xxxxxxxxxxxxx>
> ---
> drivers/gpu/drm/panthor/panthor_device.c | 1 +
> drivers/gpu/drm/panthor/panthor_device.h | 26 ++++++++++++++++++++++++
> drivers/gpu/drm/panthor/panthor_drv.c | 2 +-
> drivers/gpu/drm/panthor/panthor_sched.c | 4 ++--
> 4 files changed, 30 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/gpu/drm/panthor/panthor_device.c b/drivers/gpu/drm/panthor/panthor_device.c
> index e3b22107b268..0362101ea896 100644
> --- a/drivers/gpu/drm/panthor/panthor_device.c
> +++ b/drivers/gpu/drm/panthor/panthor_device.c
> @@ -500,6 +500,7 @@ int panthor_device_resume(struct device *dev)
>
> err_set_suspended:
> atomic_set(&ptdev->pm.state, PANTHOR_DEVICE_PM_STATE_SUSPENDED);
> + atomic_set(&ptdev->pm.recovery_needed, 1);
> return ret;
> }
>
> diff --git a/drivers/gpu/drm/panthor/panthor_device.h b/drivers/gpu/drm/panthor/panthor_device.h
> index 0e68f5a70d20..b6c4f25a5d6e 100644
> --- a/drivers/gpu/drm/panthor/panthor_device.h
> +++ b/drivers/gpu/drm/panthor/panthor_device.h
> @@ -9,6 +9,7 @@
> #include <linux/atomic.h>
> #include <linux/io-pgtable.h>
> #include <linux/regulator/consumer.h>
> +#include <linux/pm_runtime.h>
> #include <linux/sched.h>
> #include <linux/spinlock.h>
>
> @@ -180,6 +181,9 @@ struct panthor_device {
> * is suspended.
> */
> struct page *dummy_latest_flush;
> +
> + /** @recovery_needed: True when a resume attempt failed. */
> + atomic_t recovery_needed;
> } pm;
>
> /** @profile_mask: User-set profiling flags for job accounting. */
> @@ -243,6 +247,28 @@ int panthor_device_mmap_io(struct panthor_device *ptdev,
> int panthor_device_resume(struct device *dev);
> int panthor_device_suspend(struct device *dev);
>
> +static inline int panthor_device_resume_and_get(struct panthor_device *ptdev)
> +{
> + int ret = pm_runtime_resume_and_get(ptdev->base.dev);
> +
> + /* If the resume failed, we need to clear the runtime_error, which
> + * can done by forcing the RPM state to suspended. If multiple
> + * threads called panthor_device_resume_and_get(), we only want
> + * one of them to update the state, hence the cmpxchg. Note that a
> + * thread might enter panthor_device_resume_and_get() and call
> + * pm_runtime_resume_and_get() after another thread had attempted
> + * to resume and failed. This means we will end up with an error
> + * without even attempting a resume ourselves. The only risk here
> + * is to report an error when the second resume attempt might have
> + * succeeded. Given resume errors are not expected, this is probably
> + * something we can live with.
I agree this is "something we can live with", and the comment at least
explains the logic here - so hopefully it won't confuse me in the
future. But it still seems like this is the wrong solution because we've
got a known race.
On the other hand it's a clear improvement over the broken state before
(and I'm afraid I don't have time at the moment to look at it in
detail), so feel free to merge it for now:
Acked-by: Steven Price <steven.price@xxxxxxx>
> + */
> + if (ret && atomic_cmpxchg(&ptdev->pm.recovery_needed, 1, 0) == 1)
> + pm_runtime_set_suspended(ptdev->base.dev);
> +
> + return ret;
> +}
> +
> enum drm_panthor_exception_type {
> DRM_PANTHOR_EXCEPTION_OK = 0x00,
> DRM_PANTHOR_EXCEPTION_TERMINATED = 0x04,
> diff --git a/drivers/gpu/drm/panthor/panthor_drv.c b/drivers/gpu/drm/panthor/panthor_drv.c
> index 1498c97b4b85..b7a9adc918e3 100644
> --- a/drivers/gpu/drm/panthor/panthor_drv.c
> +++ b/drivers/gpu/drm/panthor/panthor_drv.c
> @@ -763,7 +763,7 @@ static int panthor_query_timestamp_info(struct panthor_device *ptdev,
> {
> int ret;
>
> - ret = pm_runtime_resume_and_get(ptdev->base.dev);
> + ret = panthor_device_resume_and_get(ptdev);
> if (ret)
> return ret;
>
> diff --git a/drivers/gpu/drm/panthor/panthor_sched.c b/drivers/gpu/drm/panthor/panthor_sched.c
> index 97ed5fe5a191..77b184c3fb0c 100644
> --- a/drivers/gpu/drm/panthor/panthor_sched.c
> +++ b/drivers/gpu/drm/panthor/panthor_sched.c
> @@ -2364,7 +2364,7 @@ static void tick_work(struct work_struct *work)
> if (!drm_dev_enter(&ptdev->base, &cookie))
> return;
>
> - ret = pm_runtime_resume_and_get(ptdev->base.dev);
> + ret = panthor_device_resume_and_get(ptdev);
> if (drm_WARN_ON(&ptdev->base, ret))
> goto out_dev_exit;
>
> @@ -3131,7 +3131,7 @@ queue_run_job(struct drm_sched_job *sched_job)
> return dma_fence_get(job->done_fence);
> }
>
> - ret = pm_runtime_resume_and_get(ptdev->base.dev);
> + ret = panthor_device_resume_and_get(ptdev);
> if (drm_WARN_ON(&ptdev->base, ret))
> return ERR_PTR(ret);
>
